1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate to which a single crystal semiconductor layer is fixed with a buffer layer interposed therebetween and a method for manufacturing a semiconductor device.
2. Description of the Related Art
Integrated circuits have been developed, which use a semiconductor substrate called a silicon-on-insulator (hereinafter also referred to as an SOI) that has a thin single crystal semiconductor layer over an insulating surface, instead of a silicon wafer that is manufactured by thinly slicing an ingot of a single crystal semiconductor. An integrated circuit using an SOI substrate has been attracting attention because parasitic capacitance between drains of the transistors and the substrate can be reduced and thus the performance of the semiconductor integrated circuit is improved.
Known examples of SOI substrates are SIMOX substrates and bonded substrates. For example, an SOI structure of a SIMOX substrate is obtained by implantation of oxygen ions into a single crystal silicon substrate and by heat treatment performed at 1300° C. or higher to form a buried oxide (BOX) layer, whereby a single crystal silicon thin film is formed on the surface.
As another method for manufacturing SOI substrates, a hydrogen ion implantation separation method is known (for example, see Reference 1: Japanese Published Patent Application No. 2000-124092). The hydrogen ion implantation separation method is a method by which hydrogen ions are implanted into a silicon wafer to form a microbubble layer at a predetermined depth from the surface, and a thin silicon layer is bonded to another silicon wafer using the microbubble layer as a cleavage plane. In addition to the heat treatment for separation of a silicon layer, it is said that it is necessary to perform heat treatment in an oxidizing atmosphere to form an oxide film over the silicon layer, remove the oxide film, and perform heat treatment at 1000° C. to 1300° C. to increase bonding strength.
Further, a method for manufacturing an SOI substrate in which a single crystal silicon layer is bonded to a glass substrate is known (for example, see Reference 2: Japanese Published Patent Application No. 2005-252244). In Reference 2, as a method for manufacturing an SOI substrate which does not need heat treatment at a high temperature exceeding 800° C., an insulating substrate is irradiated with a laser beam in order to increase bonding strength. Further, in Reference 2, mirror polishing of a single crystal silicon layer which is performed after laser beam irradiation is mentioned as a preferred embodiment mode.
Furthermore, the present applicant has disclosed a method for manufacturing a semiconductor device using Smart Cut (registered trademark), in which a substrate having high heat resistance is used as a supporting substrate, in References 3 and 4 and has disclosed a method for manufacturing a semiconductor device using Smart Cut (registered trademark), in which a light transmitting substrate is used as a supporting substrate, in Reference 5 (Reference 3: Japanese Published Patent Application No. H 11-163363, Reference 4: Japanese Published Patent Application No. 2000-012864, and Reference 5: Japanese Published Patent Application No. 2000-150905).